Figure 6.

Sodium and calcium influx occur on the rising and falling phases of the AP at near-physiological temperatures, respectively. A, Pointscan imaging protocol was performed as in Figure 4A. OGB-5N was replaced with the sodium indicator ING-2, and Alexa Fluor 594 was excluded from the internal recording solution. B, Representative ING-2 sodium imaging pointset. Points are color-coded as in panel A. Gray bar indicates the sodium transient onset and offset. C, Distribution of sodium imaging point sets calculated as in Figure 4C. Red line represents the fit of a normal distribution to the data. D, Sodium and calcium transients from pointscan imaging temporally-aligned to AP threshold and peak. Left, Sodium and calcium influx onset relative to AP threshold. Right, Sodium and calcium influx onset relative to AP peak. Transient onset time was measured for the brightest point in a point set. Circles are individual point sets. Gray dashed line shows AP threshold (left) or peak (right) timing. Red, ING-2 sodium imaging; black, OGB-5N color coded as in Figure 4; *p < 0.001, Kruskall–Wallis test with rank-sum post hoc.